Did Terrestrial Diversification of Amoebas (Amoebozoa) Occur in Synchrony with Land Plants?

Evolution of lineage diversification through time is an active area of research where much progress has been made in the last decade. Contrary to the situation in animals and plants little is known about how diversification rates have evolved in most major groups of protist. This is mainly due to uncertainty about phylogenetic relationships, scarcity of the protist fossil record and the unknown diversity within these lineages. We have analyzed the evolutionary history of the supergroup Amoebozoa over the last 1000 million years using molecular dating and species number estimates. After an origin in the marine environment we have dated the colonization of terrestrial habitats by three distinct lineages of Amoebozoa: Dictyostelia, Myxogastria and Arcellinida. The common ancestor of the two sister taxa, Dictyostelia and Myxogastria, appears to have existed before the colonization of land by plants. In contrast Arcellinida seems to have diversify in synchrony with land plant radiation, and more specifically with that of mosses. Detection of acceleration of diversification rates in Myxogastria and Arcellinida points to a co-evolution within the terrestrial habitats, where land plants and the amoebozoans may have interacted during the evolution of these new ecosystems.

谱系随时间的多样化演化是当前研究的热点领域，近十年来该领域已取得诸多进展。与动物和植物类群的研究现状不同，目前学界对绝大多数主要原生生物（protist）类群的多样化速率演化模式仍知之甚少。这一现状主要源于三大因素：系统发育关系存在不确定性、原生生物化石记录极为匮乏，以及此类谱系内的物种多样性尚未明确。我们利用分子定年与物种数量估算方法，解析了变形虫总界（Amoebozoa）过去10亿年间的演化历史。该类群起源于海洋环境后，我们通过定年分析确定了变形虫总界下三个独立谱系——网粘菌亚纲（Dictyostelia）、黏菌亚纲（Myxogastria）以及表壳目（Arcellinida）——登陆陆生生境的时间节点。作为姊妹群的网粘菌亚纲与黏菌亚纲的共同祖先，其存在时间早于植物登陆陆生环境的节点。与之形成对比的是，表壳目（Arcellinida）的多样化进程似乎与陆生植物的辐射演化同步，且更具体地与苔藓植物的辐射演化相契合。对黏菌亚纲与表壳目多样化速率加速现象的检测结果表明，陆生生境中存在协同演化关系：在这类新生生态系统的演化过程中，陆生植物与变形虫类群可能存在相互作用。